Reusable printing master and method of making same

ABSTRACT

A reusable master is produced by blanket charging an insulating carrier surface, which is intended to include a dark adapted photoconductor, toning, imagewise charging the toner, and separating the released toner from the retained toner to produce a pattern. This process makes litho masters and electrostatic masters. The toner pattern may be produced on a surface which has a very low surface attraction for grease lithographic ink, and therefore only the pattern will pick up and transfer ink. The master is reusable by dissolving away the image after use. Also, a master sheet which will not hold an electrostatic charge can be imaged, the image pattern charged and toned, and the toner thereafter transferred to plain paper. The master may be a photoconductor, which if charged in a lighted area, or flooded with light after charging, will discharge all but the toned image.

United States Patent 1191 Raschke et a1.

1451 Nov. 25, 1975 1 1 REUSABLE PRINTING MASTER AND METHOD OF MAKINGSAME ['15] Inventors: Curt R. Raschke, Warrensville Heights; Ival L.Toepke, Newbury, both of Ohio [73] Assignee: Addressograph MultigraphCorporation, Cleveland, Ohio 1221 Filed: Dec.20,1974

211 Appl.No.:534,729

[52] US. Cl. 101/463; lOl/DIG. 13; 101/425;

427/14; 427/22; 427/24 [51] Int. C1. 841M 5/00; G030 13/22 [58] Field ofSearch 427/14, 22, 24; 96/1 R,

96/1 SD, 114; 118/637; lOl/DIG. 13,453. 463, 473', 355/17 [56]References Cited UNITED STATES PATENTS 3,071,645 H1963 McNaney 355/173,405,682 10/1968 King et al. 118/637 3,443,517 5/1969 Gundlach.....101/219 3,515,584 6/1970 Yang 101/395 3,589,290 6/1971 Walkup et a1.101/426 3,632,375 1/1972 Gipe 101/450 Clark 101/DlG, l3 Rittler et a1 118/637 Primary Examiner-Michael Sofocleous Attorney, Agent, or Firm-RayS. Pyle [57] ABSTRACT A reusable master is produced by blanket chargingan insulating carrier surface, which is intended to include a darkadapted photoconductor, toning, imagewise charging the toner, andseparating the released toner from the retained toner to produce apattern. This process makes Iitho masters and electrostatic masters.

The toner pattern may be produced on a surface which has a very lowsurface attraction for grease lithographic ink, and therefore only thepattern will pick up and transfer ink. The master is reusable bydissolving away the image after use. Also, a master sheet which will nothold an electrostatic charge can be imaged, the image pattern chargedand toned, and the toner thereafter transferred to plain paper.

The master may be a photoconductor, which if charged in a lighted area,or flooded with light after charging,- will discharge all but the tonedimage.

9 Claims, 4 Drawing Figures US. Patent Nov. 25, 1975 3,921,527

"III":

whether the surface be insulating, conducting, photo- REUSABLE PRINTINGMASTER AND METHOD OF conducting.

MAKING SAME It is a further object of the invention to provide a re-BACKGROUND OF THE INVENTION Lithographic printing has developed rapidlyfrom the original stone masters to modern disposable planographicmasters.

A stride in the simplification of master material, not requiring skilledcraftsmen to produce, was the provision of a coating of clay on paperwhich can be prepared by typewriter and used on an offset press. A typedmaster will accept water and reject greasetype lithographic ink, exceptin the image area.

The master is first wet with water and then a roller having an inksurface is applied to .the master. The image alone will pick up the ink.The inked master is then rolled against a rubber mat to produce anoffset reverse image. Thereafter, the rubber mat is rolled against aplain paper sheet to produce the final printed copy.

Typing such a master greatly facilitated the printing art by makingquality printing available to much lower skilled personnel.Nevertheless, the direct image master has limitations. Hence, aselectrostatic copy techniques became well developed, means weredeveloped to chemically convert a developed copy sheet into alithographic master.

Electrostatic copy sheets made of zinc oxide are oleophilic. After beingdeveloped and an image fused to the surface, the zinc oxide may beconverted to an oleophobic condition by chemical reaction with aconversion solution. The image will not be converted because it is aninert material. It will accept grease ink, but the background willreject grease ink when wet.

Masters which must be converted usually are quite high in printingquality. However, the preparation of a photoconducting coating is anexacting process and sometimes not successful. The reason for failure isnot always easy to identify. Usually, the failure is evidenced by ageneral gray toning of the area which should be free of ink.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration ofapparatus suitable to carry out the method of this invention;

FIG. 2 is a section taken along line 2-2 of FIG. 1; FIG. 3 is a sectionthrough a representative suitable master sheet; and

FIG. 4 is an illustration of an alternative adaptation of the struturein FIG. 1.

SUMMARY OF THE INVENTION This invention and the development by otherprior inventors is based upon the premise that a surface which isnaturally oleophobic will not be subject to the incorporeal influenceswhich plague the conversion step in conventional master technique.

The problem is to provide such a surface with an ink accepting image, oran image which may be electrostatically charged and toned.

Therefore, an object of this invention is to provide a commerciallyacceptable image-producing process for imaging a stable oleophobic,hydrophilic master sheet surface.

A further object of this invention is to provide a reproducible masterimage on substantially any surface,

usable master in order that the costs of the master sheet may be appliedto several or many printing cycles of different context. In thisrespect, it is the object to reduce the cost of master use and theconsequent reduction of solid waste material.

It is further an object of this invention to provide a master suitablefor duplicating electrostatic copies as described in U.S. Pat. Nos.3,271,146 and 3,795,442. If a master is prepared with a fused image ofinsulating toner on a conducting or semi-conducting surface (such asmetal or zinc oxide), the fused image can be charged, toned, and theunfused toner transferred to paper many times to serve as a duplicator.

DESCRIPTION OF THE PREFERRED EMBODIMENT The original stone lithographyis a direct image process that is highly successful, but requires a veryexpensive master in that each stone must be laboriously processed and isuseful for one original image only. Such a lithographic process employsa type of stone which when wet has a very low adhesion for ink, and theengraved image to be reproduced actually holds ink in the recess of theengraved image and will transfer some of that ink to a carrier sheetpressed against the surface of the stone.

Because such a stone is a slow and wasteful mastermaking process, themany well-known techniques were developed for planographic printingwherein such easily obtainable materials on aluminum and zinc are usedas a master sheet with various means converting that sheet into areaswhich reject grease ink and those areas which accept the grease ink,thereby making possible a differential to produce an ink image. The inkis then carried in image form by such a master.

Later, direct image masters, which are essentially clay compositionsheld by synthetic resin binders, replaced the more expensive metalmasters. These clay I masters are typed in a conventional typewriterusing a ribbon of grease type release ink in order to type an adherentgrease image on the master sheet. Then, when the master sheet is wetwith starter fluid, the background will not accept grease ink, but thetype image will. Thus, by repeating an application of moisture andthereafter an application of ink to the surface of this master, theimage will pick up and transfer the grease type ink to animage-receiving surface. If the image is applied to a blanket and thento a receiving sheet, the image will be reversed on the blanket and thenright reading on the final receiving sheet. Such masters are relativelyinexpensive but are discarded after each use and also subject to thesometimes unexplainable vagrancies which upset the system and fail toproduce good results. Such failures are rare but do exist.

Inventors have long made an effort to provide a lithography system thatwould produce an easily made master but would not require a delicatebalance of moisture and ink. Two such patents are illustrated by U.S.Pat. Nos. 3,677,178 and 3,511,178.

These prior references have approached the basic problem of eliminatingthe need for conversion and moisture by taking advantage of the naturalink-rejecting characteristics of silicone rubber. By selecting an inkand polysiloxane combination of related characteristics, a master sheetcoated with a thin layer of polysiloxane will not accept an ink ofsufficient surface tension. A grease type ink will usually provide thelow adhesive attraction for polysiloxane surfaces.

Curtain US. Pat. No. 3,511,178 provided the image by causing image areasof a non-ink receptive surface to wash away, exposing a highly inkreceptive surface in image configuration to be exposed in a backgroundwhich is ink-rejecting. Gipe US. Pat. No. 3,677,178 improved somewhat onthe means to produce such image cavities in a polysiloxane field.

Sorkin US. Pat. No. 3,775,1 provided a means for producing anelectrostatic image under the polysiloxane surface, and thereby set up afield effect to hold a toner on the polysiloxane surface until fused.This development elimated the need for processing the polysiloxanesurface to wash away an image portion thereof, but does require anundercoating of photoresponsive material for each master. The tonedimage will carry ink for impressing on a receptive carrier.

The present invention employs an ink-rejecting surface master sheet andestablishes an image in an improved manner over these prior artteachings. One very suitable surface is a polysiloxane materiial, whichhas a very low adhesion for grease type printing ink. The patentee ofUS. Pat. No. 3,511,178 characterizes such a surface as being adhesive.Other suitable surfaces are Teflon and polyethylene.

FIG. 3 of the drawing is representative of the cross section of a mastersheet according to this invention. A dimensionally stable base sheet Amay be of a selected one of many suitable materials, such as aluminum,paper, or dimensionally stable man-made plastic material. A coating B ofpolysiloxane of the type amply disclosed and discussed by Curtain US.Pat. No. 3,51 1,178, which is expressly incorporated herein byreference, will provide the adhesive coating.

The apparatus and method for making a reusable master according to thisinvention is illustrataed schematically in FIG. I. The actual apparatusis sufficiently similar to electrostatic copying and duplicatingmachines that this schematic illustration will be sufficient for thoseskilled in the art.

A belt 10 is made of a conducting backing 12. The backing is preferablymetal. The backing 12 is coated with a dielectric surface 14. Theselected dielectric will accept a static electric charge on the surfacethereof and not lose that charge over an extended period of time. TheDupont Corporation is a source of several such materials. Teflon is onesuch material which is satisfactory, and this is the trademark of theDupont Corporation for a product known chemically aspolytetrafluoroethylene. Mylar is a Dupont trademark for polyester film.

The belt 10 is shown as a horizontal endless belt reaved around tworollers 16.

The method to be carried out to produce a temporary image for transferto the polysiloxane, Teflon, or polyethylene master surface isaccomplished by flooding the surface 14 with a uniform charge by meansof a corona device 20. A corona device is well-known in the photocopyart and consists usually of a wire or braid of wire behind a reflectorand connected to a source of high voltage.

After the dielectric surface 14 is flooded with a charge, whethernegative or positive it does not matter, the charge is uniformly tonedby means of any conventional toning device, using a toner compatiblewith the sign of the charge, illustrated as being a magnetic brush 22.Cascading and other types of toning systems are optional. An example ofa brush toner may be seen in U.S. Pat. No. 3,387,586. The brush 22operates to pick up and supply toner from a toner supply sourceillustrated diagrammatically by a container 24.

The belt can be toned directly without a corona precharge, if a biasedmagnetic brush is used. In this case the brush is biased relative to theback of the insulating belt in a manner to force the charged tonerparticles onto the insulation. (Positive, relative to the belt, ifpositive toner used, and negative if negative toner used.)

The next step in the method is to release toner from the uniformly toneddielectric surface 14 in an image configuration which is to be copied orreproduced. A stencil screen 30 is illustrated as an ion modulatingdevice to filter out a stream of ions produced by a corona device 32.The stencil screen 30 is illustrated as a reusable photoconductor screenbut may literally take the form of a metal stencil with the imagepattern cut in the metal. The ion discharge produced by the coronadevice 32 is then permitted to pass through the stencil only in thepassages provided by the cut pattern in the stencil.

The preferred photoconducting screen 30 consists of a photoconductorcoated on a fine metal screen. An imaging system 31 will create areascharged in such a manner as to repel ion flow and other areas unchargedor discharged in an image pattern to allow the passage of the ionsproduced by the corona device 32. These devices are known and arementioned only as examples.

The stencil screen 30 is moved into position over the upper run of thebelt 10 and the corona device 32 caused to emit a pattern of ionparticles through the screen to the belt surface to neutralize thosecharges produced by the uniform deposition of the corona device 20. Thisresults in a field of toner particles in which the background isuniformly adhering to the belt surface by means of the electrostaticcharge, and an image area within the field wherein the toner is loosebecause of a discharge of the image-holding field.

Thus, the belt 10 is advanced to a station 34 where a pressure roller 36presses a previously prepared master shown in FIG. 3 against the surface14 and causes the loose image area toner to adhere to the polysiloxanesurface. If necessary or desirable, a field device may be establishedbehind the master sheet to help attract the toner from the surface 14 tothe polysiloxane surface.

After transfer of the image to the master sheet, the master may betreated by any device for fixing the toner in a known manner. Pressure,heat and/or solvent fixing are devices well-known in the art.

After the image has been lifted from the surface of the belt 10, thebelt then proceeds around the end of the roller 16 and the areaspreviously neutralized are re-flooded with a new charge from the coronadevice 20 and if the charge on the balance of the background has becomeweak, the strength of the charge is reinforced. Then the belt is retonedin the manner described, and prepared for a second imprint.

The prepared master is used in any suitable lithographic orelectrostatic printing apparatus whether offset or direct image.Although usually not necessary, some moisture may be employed in thelithographic mode if that is believed desirable to improve and assurequality.

At the end of the use of the prepared master, rather than discarding themaster, the surface may be flooded with a solvent for the toner resinbinder in order to dissolve the image and restore the polysiloxanemaster surface to a clean state for reuse. Toner mixes usually employcarbon and a fusable resin which holds the carbon particles in position.Such resins are soluble in a number of petroleum and alcohol solvents,and are thus removable.

FIG. 4 is an alternative method of producing masters by the principlesof this invention, and also illustrates a means for making a negativemaster wherein the background is ink-receptive and the image isink-rejecting.

The apparatus of FIG. 4 is essentially the same as that in FIG. 1 exceptthat the belt, designated herein as belt 50, is not an electrostaticbelt but is designed only to carry masters represented by symbols 52 and53in FIG. 4. A looped endless belt is not essential but is in harmonywith FIG. 1 and will illustrate the principles. A vacuum belt,mechanical adhesion or any other means is employed to carry the masters52 and 53 on belt 50.

The masters pass the corona discharge station and are thenblanketed-toned by the brush 22. Thereafter the stencil screen operatesas described with respect to FIG. 1 to release a pattern of the tonerparticles.

This embodiment differs in that the image area is lifted from thesurface of the masters rather than the background. Hence, the mastersare caused to run under a roller 60. Roller 60 could operate either as amechanical adhesion device to attract the particles, or may be assistedby a field effect produced from within the roller to help lift away theloosened toner material. The result is a master with a uniformly tonedbackground and a non-toned image area. This master may be used toproduce an inked background with a blank image area, or printing areasmay be provided which are negative working and will adhere to the imagearea in preference to the background.

In either event, whether the master is made by the process and apparatusof FIG. 1 or FIG. 4, conventional fusing is employed to bind the imageto the surface of the master, and after use, the toner material may thenbe dissolved in a suitable solvent for reuse of the master.

EXAMPLE l An endless belt of aluminized mylar was uniformly charged to+700v with a positive corona and toned uniformly with a bias electrodedcascade developer, using Xerox 914 developer mix. The toned belt wasthen imaged with a negative corona directed through the stencil to thetoner layer. The negative image charge leaked through the toner andneutralized the positive charge on the belt, loosening the toner in animagewise fashion.

The imagewise loosened toner was then transferred to a polysiloxanesurface. This was accomplished by placing the polysiloxane in contactwith the imaged belt and running them between conducting pressurerollers biased to keep the charged background toner on the mylar belt.The loosened toner transferred by pressure to the polysiloxane sheet.

The toned polysiloxane sheet was then fused and used to printlithographic copies.

After use, the polysiloxane sheet was scrubbed with acetone whichdissolved the toner but did not dissolve the polysiloxane. After drying,the polysiloxane sheet was ready to receive another image.

EXAMPLE 2 A thin sheet of Teflon (tetrafluoroethylene) with an aluminumbacking was uniformly toned using a mag netic brush ofAddressograph-Multigraph Type D Electrostatic Developer Mix. The brushwas biased to +l00v relative to the aluminum backing and deposited toneron the initially uncharged Teflon.

The toner layer was then uniformly charged with a positive corona andthen imagewise charged with a negative corona directed through a stencilmodulator to the belt. The magnitude of the deposited image negativecharge density was several times that of the uni form positive chargedensity.

The imagewise charged toner was then transferred to a receiving rollerwhich was biased positively to the alu' minum backing to pick up theimage charged toner and repel the background toner.

The background toner remaining on the Teflon sheet was heat-fused to thesheet and negative lithographic copies printed from it.

After use, the Teflon sheet was scrubbed with methylene chloride whichdissolved the toner but did not dissolve the Teflon. After drying, theTeflon sheet was ready to receive another image.

EXAMPLE 3 A receiving surface was toned as in Example 2. It was apolyethylene surface for the lithographic master and a metal surface forthe dry electrostatic master case.

In one test, the uniformly toned surface was then imagewise charged by anegative corona directed through an ion modulator to the toner and inanother test, a positive corona was used. Enough image charge wasdeposited to pin-down the toner on the sheet and the loosely boundbackground toner removed with a blast of air.

The remaining image toner was then heat-fused to the receiving surfaceand copies printed from the master. Lithographic copies were made fromthe toned polyethylene plate and dry electrostatic copies from the tonedmetal plate.

What is claimed is:

l. The method of making a lithographic master, comprising the steps of:

1. providing a flexible carrier support sheet having an oleophobic layeradhered thereto which is highly repellent to oil based ink, saidoleophobic layer having an adhesive release value, when dry, of lessthan about grams per square inch and being an electrically insulatedmaterial selected from the class of ink release surface materialsconsisting of a cured elastomeric organopolysiloxane,tetrafluoroethylene, and polyethylene;

2. creating a blanket electrostatic charge on said carrier support sheetand uniformly toning said sheet with a triboelectric toner;

3. thereafter, subjecting said toned support sheet to a pattern ofelectrostatic charge to neutralize the electrostatic holding power thusforming loose toner in a pattern formation;

4. providing a transfer surface having a mechanical affiliation for saidloose toner in the pattern formation, and placing said transfer surfaceagainst said toned support sheet bearing the loose toner pattern toseparate the toner into one surface with a negative image and the otherwith a positive image; and

5. finally, fixing the image to the carrier to produce a lithographicmaster.

2. In the method defined in claim 1, the carrier support sheet being acontinuous belt, and the transfer surface picking up a positive image.

3. In the method of claim 2, said transfer surface being a dry,semi-conducting electrostatic master.

4. In the method of claim 1, the oleophobic layer being polysiloxanehaving a low adherence for grease lithographic ink.

5. [n the method of claim 1, the final step of dissolving the fixedimage to reuse the carrier support sheet.

6. In the method of claim I, producing the pattern of electrostaticcharge by use of ion modulators.

7. The method of making a lithographic master, comprising the steps of:

1. providing an electrically insulating flexible carrier support sheethaving an oleophobic layer adherent thereto which is highly repellent tooil-based ink, said oleophobic layer being further characterized ascomprising a cured elastomeric organopolysiloxane having an adhesiverelease value, when dry, of less than about lOO grams per inch;

2. creating a blanket electrostatic charge on said carrier sheet andapplying a uniform coating of a triboelectric toner thereon held by saidcharge;

3. thereafter, subjecting said toned surface to a pattern of electrosticcharge to neutralize the electrostatic holding power thus forming loosetoner in a pattern formation;

4. separating said loose toner in said pattern formation from said tonedsurface to create a remainder pattern of toner which may be transferredto a surface having an olephobic layer adherent thereto which is highlyrepellent to oil-based ink, said olephobic layer being selected from theclass of ink release surface materials consisting of a cured elastomeric organopolysiloxane, tetrafluoroethylene, and polyethylene,having an adhesive release value, when dry, of less than about lOO gramsper square inch; and

5. finally fixing the toner on the carrier support to produce anoleophobic master.

8. In the method of claim 7, said transfer surface being a dryelectrostatic master.

9. [n the method of claim 7, the method of producing the pattern ofelectrostatic charge by use of ion modu-

1. PROVIDING A FLEXIBLE CARRIER SUPPORT SHEET HAVING AN OLEOPHOBIC LAYERADHERED THERETO WHICH IS HIGHLY REPELLENT TO OIL-BASED INK, SAIDOLEOPHOBIC LAYER HAVING AN ADHESIVE RELEASE VALUE, WHEN DRY, OF LESSTHAN ABOUT 100 GRAMS PER SQUARE INCH AND BEING AN ELECTRICALLY INSULATEDMATERIAL SELECTED FROM THE CLASS OF INK RELEASE SURFACE MATERIALSCONSISTING OF CURED ELASTOMERIC ORGANOPOLYSILOXANE, TETRAFLUOROETHYLENE,AND POLYETHYLENE;
 1. THE METHOD OF MAKING A LITHOGRAPHIC MASTER,COMPRISING THE STEPS OF:
 2. CREATING A BLANKET ELECTROSTATIC CHARGE ONSAID CARRIER SUPPORT SHEET AND UNIFORMLY TONING SAID SHEET WITH ATRIBOELECTRIC TONER;
 2. creating a blanket electrostatic charge on saidcarrier sheet and applying a uniform coating of a triboelectric tonerthereon held by said charge;
 2. In the method defined in claim 1, thecarrier support sheet being a continuous belt, and the transfer surfacepicking up a positive image.
 2. creating a blanket electrostatic chargeon said carrier support sheet and uniformly toning said sheet with atriboelectric toner;
 3. In the method of claim 2, said transfer surfacebeing a dry, semi-conducting electrostatic master.
 3. thereafter,subjecting said toned surface to a pattern of electrostic charge toneutralize the electrostatic holding power thus forming loose toner in apattern formation;
 3. THEREAFTER, SUBJECTING SAID TONED SUPPORT SHEET TOA PAT TERN OF ELECTROSTATIC CHARGE TO NEUTRIALIZE THE ELECTROSTATICHOLDING POWDER THUS FORMING LOOSE TONER IN A PATTERN FORMATION; 3.thereafter, subjecting said toned support sheet to a pattern ofelectrostatic charge to neutralize the electrostatic holding power thusforming loose toner in a pattern formation;
 4. PROVIDING A TRANSFERSURFACE HAVING A MECHANICAL AFFILIATION FOR SAID LOOSE TONER IN THEPATTERN FORMATION, AND PLACING SAID TRANSFER SURFACE AGAINST SAID TONERSUPPORT SHEET BEARING THE LOOSE TONER PATTERN TO SEPARATE THE TONER INTOONE SURFACE WITH A NEGATIVE IMAGE AND THE OTHER WITH A POSITIVE IMAGE;AND
 4. separating said loose toner in said pattern formation from saidtoned surface to create a remainder pattern of toner which may betransferred to a surface having an olephobic layer adherent theretowhich is highly repellent to oil-based ink, said olephobic layer beingselected from the class of ink release surface materials consisting of acured elastomeric organopolysiloxane, tetrafluoroethylene, andpolyethylene, having an adhesive release value, when dry, of less thanabout 100 grams per square inch; and
 4. providing a transfer surfacehaving a mechanical affiliation for said loose toner in the patternformation, and placing said transfer surface against said toned supportsheet bearing the loose toner pattern to separate the toner into onesurface with a negative image and the other with a positive image; and4. In the method of claim 1, the oleophobic layer being polysiloxanehaving a low adherence for grease lithographic ink.
 5. In the method ofclaim 1, the final step of dissolving the fixed image to reuse thecarrier support sheet.
 5. finally, fixing the image to the carrier toproduce a lithographic master.
 5. FINALLY, FIXING THE IMAGE TO THECARRIER TO PRODUCE A LITHOGRAPHIC MASTER.
 5. finally fixing the toner onthe carrier support to produce an oleophobic master.
 6. In the method ofclaim 1, producing the pattern of electrostatic charge by use of ionmodulators.
 7. The method of making a lithographic master, comprisingthe steps of:
 8. In the method of claim 7, said transfer surface being adry electrostatic master.
 9. In the method of claim 7, the method ofproducing the pattern of electrostatic charge by use of ion modulators.